Inhibition of human dental pulp stem cell differentiation by Notch signaling

Notch signaling plays a critical role in development and cell fate specification. Notch receptors and ligands have been found to be expressed in dental epithelium or mesenchyme in the developing tooth, suggesting that Notch signaling may regulate odontogenesis. Post-natal human dental pulp stem cells (DPSCs) isolated from the dental pulp have characteristics of mesenchymal stem cells and can differentiate into odontoblasts. In this study, we examined whether Notch signaling regulated the odontoblastic differentiation of DPSCs. We found that over-expression of the Notch ligand, Jagged-1, activated the Notch signaling pathway in DPSCs. Jagged-1 inhibited the odontoblastic differentiation of DPSCs in vitro. Jagged-1-expressing DPSCs could not form mineralized tissues in vivo. Moreover, over-expression of the constitutively activated Notch1 intracellular domain (Notch-ICD) also inhibited odontoblastic differentiation of DPSCs. Taken together, our results demonstrate that Notch signaling can inhibit the odontoblastic differentiation of DPSCs.

Wnt/beta-catenin inhibits dental pulp stem cell differentiation

Dental pulp stem cells (DPSCs) are a unique precursor population isolated from postnatal human dental pulp and have the ability to regenerate a reparative dentin-like complex. Canonical Wnt signaling plays a critical role in tooth development and stem cell self-renewal through beta-catenin. In this study, the regulation of odontoblast-like differentiation of DPSCs by canonical Wnt signaling was examined. DPSCs were stably transduced with canonical Wnt-1 or the active form of beta-catenin, with retrovirus-mediated infection. Northern blot analysis found that Wnt-1 strongly induced the expression of matricellular protein osteopontin, and modestly enhanced the expression of type I collagen in DPSCs. Unexpectedly, Wnt-1 inhibited alkaline phosphatase (ALP) activity and the formation of mineralized nodules in DPSCs. Moreover, over-expression of beta-catenin was also sufficient to suppress the differentiation and mineralization of DPSCs. In conclusion, our results suggest that canonical Wnt signaling negatively regulates the odontoblast-like differentiation of DPSCs.

Stromal cells in haemopoiesis

Stromal cells of the bone marrow can provide the growth-promoting and differentiation-inducing molecules which are necessary for haemopoiesis. While the nature of these stimuli is largely unknown, the development of haemopoietic cells in association with stromal cells requires intimate cell contact. Molecules of the extracellular matrix, such as heparan sulphate, are able to bind growth factors and in this way the stromal cells may form microenvironmental niches which preferentially promote development of multipotent and committed cells along discrete lineages. Cells from some patients with acute and chronic myeloid and lymphoid leukaemias are defective in their ability to interact with stromal cells and consequently cannot survive in stromal cell-mediated long-term marrow cultures. We have exploited this phenomenon to obtain normal haemopoietic cells from patients with leukaemia, and to use these cells for successful autografting in patients with acute and chronic myeloid leukaemias.

Cadmium accumulation in the human retina: effects of age, gender, and cellular toxicity

Tobacco smoking and aging are among the few factors linked to age-related macular degeneration (AMD), a major cause of blindness in the elderly. Recent studies indicate that cadmium (Cd), an environmental toxic trace metal, is approximately four-fold higher in the retinas of smokers compared to non-smokers. In this study, we determined the effects of age and gender on Cd accumulation in human retinal tissues, specifically the neural retina, retinal pigment epithelium (RPE), and choroid. Cadmium levels in cultured RPE cells or retinal tissues isolated from frozen donor eyes were measured using inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrophotometry (GF-AAS). Cadmium uptake in cultured human RPE cells (ARPE-19) was also assessed using GF-AAS. Toxic effects of cadmium were determined from cell loss (measured as a decrease in cell density) and lactate dehydrogenase release (an indicator of membrane disruption). In "young" eyes (< 55 years) Cd was highest in the retinal pigment epithelium and lowest in the neural retina. Cd was higher in all tissues in aged eyes (>or=55 years) and was significantly higher in the neural retina and RPE in older females. Cultured RPE cells exposed to Cd showed altered cell morphology, decreased cell survival, elevated ROS levels and concentration-dependent disruption of membrane integrity. We conclude that cadmium is accumulated differently in the neural retinal and RPE of older men and women. The deleterious effects of Cd on RPE cells indicate that this environmental toxin is a potentially important factor in age-related retinal disease.

Characteristics of a high-risk minority population

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Background: Black and Hispanic breast cancer patients have a worse outcome when compared to Caucasians. This could be due to socioeconomic, cultural or biologic factors. We hypothesized that host and tumor biologic characteristics associated with a poor outcome may be found more often in minority women. Methods: Race/ethnicity, menopausal status, tumor histological features, and patient characteristics including age and body mass index (BMI) were reviewed from a prospective neoadjuvant trial of docetaxel vs. doxorubicin/cyclophosphamide at Baylor College of Medicine Breast Center, from September 2002 to September 2006. The data were analyzed using Chi-square and Fisher's exact tests, while the Kruskal-Wallis method was used to analyze BMI. Results: Of the 167 patients, 63% (n=105) were Caucasian, 15% (n=26) were Hispanic and 22% (n=36) were Black. The mean age was 47.6 years (range: 30–72). Fifty-nine percent were premenopausal. Overall, mean BMI was 29, with Caucasians having a mean BMI of 27.5, Hispanics with 29.8 and Blacks with a BMI of 34.6 (P<0.001). Sixty-five percent of the Caucasians and 58% of Hispanics were ER+ or PR+ versus 44% of Blacks (P=0.09). Sixteen percent of Caucasians were HER-2 positive compared to 4% of Hispanics and 9% of Blacks (p=0.25). In addition, 22% of Caucasians and 38% of Hispanics were ER-, PR-, HER-2- compared to 50% of tumors from Blacks (p=0.007). There was a trend linking BMI and triple negative status in breast cancers, which did not achieve statistical significance (p=0.21). Conclusion: In this study we found that black and Hispanic women were more likely to be obese and have ER-, PR-, HER-2- tumor phenotypes, both of which have been associated with poorer outcomes. Ongoing studies are being performed to elucidate the link between clinical and biological characteristics and understand the underlying molecular mechanisms associated with these findings.

No significant financial relationships to disclose.

Identifying patients at high risk for neutropenic complications during chemotherapy for metastatic breast cancer (MBC) with doxorubicin or pegylated liposomal doxorubicin: Development of a prediction model

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Background: Despite the effectiveness of anthracycline (ACH) therapy in the adjuvant and MBC settings, neutropenic complications (NC) remain a common and often unpredictable problem. Consequences may include dose reductions or delays in chemotherapy, or hospitalization for fever or infection. This study describes the development of a cycle-based risk prediction model for NC during chemotherapy with traditional doxorubicin (DOX) or a pegylated liposomal formulation (PLD) for MBC. Methods: Data analyzed was from a randomized clinical trial of MBC patients (n=509), who received chemotherapy with DOX (60 mg/m2 every 3 wks) or PLD (50 mg/m2 every 4 wks) [O'Brien, 2004]. NC were defined as an absolute neutrophil count (ANC) = 1.5 x106 cells/L, febrile neutropenia or neutropenia with infection. Patient, treatment and hematological factors potentially associated with NC were evaluated. Factors with a p-value of ≤ 0.25 within a cycle were included in a generalized estimating equations (GEE) regression model. Using backward elimination, we derived a risk scoring algorithm (range 0–63) from the final reduced model. Results: Risk factors retained in the model included poor performance status, ANC = 2.0 × 106 cells/L at some point in the previous cycle, the first cycle of chemotherapy, DOX vs. PLD and older age. A precycle risk score from = 25 to < 40 for a given patient was identified as being the optimal threshold for sensitivity (58.0%) and specificity (78.7%). Patients with a score at or beyond this threshold would be considered at high risk for developing NC in later cycles. Risk scores below, within, or above this threshold predict a 0.3%–2%, 3%–8% and a 9%–45% probability risk of NC, respectively. Conclusion: This risk prediction tool demonstrated acceptable internal validity and can be readily applied by the clinician prior to a given cycle of chemotherapy. The application of this prediction tool may allow for identification and targeted intervention (such as growth factor support or the use of PLD) for those most likely to experience NC during anthracycline-based chemotherapy for MBC.

No significant financial relationships to disclose.

A genomic signature of chemotherapeutic multidrug resistance provides a rational approach to identify patients for targeted therapy in advanced solid tumors

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Background: Multidrug resistance (MDR), the process by which cells resist many structurally and functionally unrelated drugs, remains a major challenge for cancer treatment. Strategies to reliably predict MDR will revolutionize cancer therapy. Methods: We made use of in vitro drug sensitivity data on 47 FDA approved chemotherapeutic agents from the NCI-60 database coupled with Affymetrix microarray data, to develop a gene expression signature of chemotherapeutic MDR, using a 'metagene’ approach to gene expression analysis (Potti et al, Nature Medicine, 2006). The capacity of the MDR signature to predict in vitro and in vivo resistance was evaluated in multiple independent cell line and patient cohorts. Results: A gene expression signature of chemotherapeutic MDR developed from cancer cell lines using a novel ‘metagene’ approach can accurately predict patients resistant to standard chemotherapeutic agents, including multi-drug regimens. This includes cohorts of patients with early stage breast cancer (n = 171; accuracy: 75.5%, sensitivity: 49.3%, specificity: 92%), patients who received neoadjuvant chemotherapy (n = 51; accuracy: 78.5%, sensitivity: 73.7%, specificity: 92.3%), and ovarian cancer (n = 105; accuracy: 83.8%, sensitivity: 71.8%, specificity: 93.7%). We further show that MDR signature expression is an independent prognostic factor in early stage breast cancer (p = 0.02, odds ratio: 3.49) and a large cohort of non-small cell lung cancer (p = 0.03, odds ratio: 5.70), in a multivariate analysis. Finally, to identify a rational therapeutic strategy in patients with the MDR phenotype, we have integrated the prediction of MDR with profiles of oncogenic pathway deregulation (Bild A, Nature, 2006) and show that targeting the Src pathway using a Src specific inhibitor (SU6656) circumvents MDR in the in vitro setting. Conclusions: The development of a gene expression signature of MDR, that can predict resistance to commonly used cytotoxic chemotherapies, provides a rational approach to developmental therapeutics, by identifying novel 'customized’ candidate drugs (e.g. targeting Src) for further clinical development.

No significant financial relationships to disclose.